#3371 Postby srainhoutx » Wed Jan 21, 2015 8:36 am
Morning briefing from Jeff:
Strong storm system will bring impacts to SE TX over the next 48 hours.
Upper level trough over the SW US will deepen (intensify) and move eastward into the southern plains on Thursday and Friday. A weak surface cold front will cross the region this morning helping to scour out the dense sea fog, but clouds will linger over the region and highs today will be 5-10 degrees colder than yesterday in the low to mid 60’s.
Rapid changes onset this evening as combined deep Pacific moisture tap and Gulf moisture begin to overrun the surface cold dome. Coastal surface trough/low will be forced near the middle TX coast early Thursday as strong height falls overspread TX from the west. Moisture values soar through the roof overnight with values at CRP approaching the climatological maximum for middle January with PWS surging to over 1.50 inches and nearing 1.75 inches. This is nearly summer moisture being worked on by wintertime dynamics…so it is going to rain and rain a lot!
Will onset light rain and showers this evening from west to east across the area with rainfall really ramping up after midnight into early Thursday as the coastal low deepens off the middle coast swinging copious moisture inland. Instability is lacking so not expecting much if any thunder, but widespread waves of light to moderate rainfall with bands of heavy rainfall is likely from after midnight to early afternoon of Thursday.
Rainfall Amounts:
GFS model output is showing a solid 2.0 inches across much of the area and given the “excessive” moisture values that will be in place this is certainly likely. Will go with widespread 1.5-2.5 inches with isolated totals of 3.0 inches. Virtually the entire area will see a good soaking rainfall, but the area along and south of US 59 stand the best shot at heavy rainfall especially Thursday morning. Even though moisture levels will approach maximum values, the lack of sustain deep convection (limited instability) should preclude short term excessive rainfall rates.
Widespread nature of the rainfall combined with already moist soils will generate run-off from this event into area watersheds and rivers. Main threat will be minor street flooding during period of heavy rainfall.
Marine:
Coastal system (low) deepens as it crosses our coastal waters Thursday/Friday. NE winds will stiffen today and then shift to ENE and increase more on Thursday. Sustained winds of 15-25mph will be likely on Thursday and this will increase to 20-30mph Thursday night as the pressure gradient tightens. This is a favorable wind direction for coastal water level rise on the upper TX coast and expect tides to begin to increase Thursday morning and peak Thursday evening before winds shift around to the NW and offshore. Current extra-tropical storm surge guidance based on the GFS model run shows both Galveston and Sabine Pass approaching 2.0 ft of total water level rise Thursday evening with almost a foot being storm surge. These levels are below critical coastal flood elevations, but will put water well up to beaches and into low lying areas. Wave run-up especially on the backside (north) of Galveston Island and the west side of Galveston Bay may result in minor coastal overwash of bulkhead protection. Could see near gale force wind gust Thursday night and Friday morning as the low pressure system moves toward the Louisiana coastal waters. Coastal water levels will rapidly fall Friday morning with strong offshore flow.
Temperatures:
Cold air advection will remain in place throughout this event with the warm sector remain far out over the Gulf waters. Temperatures will remain steady in the 40’s on Thursday and Friday. Cold portion of the main upper trough passes nearly overhead Friday afternoon with at least one model showing critical thickness values being reached for some winter precipitation north of HWY 105. Will disregard this potential at this time due to warm surface temperatures and lack of any other support from other model guidance.
Weekend:
It will be all over and done late Friday with another very nice weekend expected as the storm system departs to the east. Skies will clear Saturday with only some high clouds spilling across the region. Temperatures will range from the 30’s for lows to the 60’s for highs.
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